Inductive-capacitive probe in machine for handling sheetlike material

ABSTRACT

Machine for handling sheetlike material, such as a printing press and a sheet feeder therefor, having a combined inductivecapacitive probe for discriminating among the presence of a single thickness of the sheetlike material, the absence of the material, and the presence of excessively thick sheetlike material, such as two or more superimposed sheets, or for determining the moisture content of the sheetlike material. The probe is substantially insensitive to machine vibrations.

United States Patent Inventors Appl. No.

Filed Patented Assignee Walter E. Dauterman Willowick;

George Y. Ono, Mayfield Heights, both of Ohio Dec. 3, 1968 Sept. 28, 1971 Harris-Intertype Corporation Cleveland, Ohio INDUCTlVE-CAPACITIVE PROBE IN MACHINE FOR HANDLING SHEETLIKE MATERIAL 10 Claims, 4 Drawing Figs.

US. Cl 340/259, 324/61, 340/258 C Int. Cl ..G08b2l/00, B65h 25/14 Field of Search 340/259,

References Cited UNITED STATES PATENTS Roggenstein Greene Wiprud Domeier et a1.

Chesney et al.. Kolb Primary Examiner-John W. Caldwell Assistant Examiner- Perry Palan Attorney-Yount, Flynn & Tarolli 324/61 UX 340/258 UX 340/259 X 340/258 UX 340/258 X 340/259 ABSTRACT: Machine for handling sheetlike material, such as a printing press and a sheet feeder therefor, having a combined inductive-capacitive probe for discriminating among the presence of a single thickness of the sheetlike material, the absence of the material, and the presence of excessively thick sheetlike material, such as two or more superimposed sheets, or for determining the moisture content of the sheetlike material. The probe is substantially insensitive to machine vibrations.

4/- E40 OUTPUT PATENIED sires |97I m a m 0 WW W m MW of 6% W m u F I llllllllll law l|l|I|l.|.|.|l-l||11 4 w E M A m D VOLTAGE OUTPUT lNDUCTIVE-CAPACITIVE PROBE IN MACHINE FOR HANDLING SHEETLIKE MATERIAL The present invention relates to machines for handling sheetlike material, such as single or superimposed sheets or webs of flexible material, such as paper, or pieces of relatively stiff material, such as cardboard, wherein the sheetlike material is advanced to a sensing station at which is located a sensing probe for sensing the presence or absence of the sheetlike material or its thickness or moisture content.

Sheet-feeding mechanisms of the stream type are commonly used with printing presses and, when so used, the sheets of the stream successively move to a registering position, from which they are taken and delivered to the printing press. The sheets of the stream may be separated from each other so that the sheets are not overlapped or the stream may be a lapped stream composed of either overlapped or underlapped sheets. For printing presses and certain other sheet-handling machines for operating on sheets received from the stream, it is important that only one sheet at a time move to a position from which it is taken into the machine and that the sheets arrive in proper time with respect to the operation of the sheethandling machine. One aspect of the present invention is directed to providing an improved sensing probe for such machines.

Another aspect of the present invention is directed to the detection of web breakage in a web handling machine, such as a web press.

An important object of the present invention is to provide in a machine for handling sheetlike material a novel and improved sensing probe which does'not contact the sheetlike material. The probe senses the sheetlike material to determine, for example, whether the sheetlike material has or has not arrived at the sensing probe, or to determine the number of layers of the sheetlike material at the probe, or to detect web breakage.

Another object of the present invention is to provide in a machine for handling sheetlike material a novel sensing probe whose response is substantially insensitive to machine vibrations which may be causing changes in the spacing between the sheetlike material and the probe.

Another object of this invention is to provide in a machine for handling sheetlike material a novel sensing probe which combines inductive and capacitive probe elements arranged to substantially nullify the effects of machine vibrations on the probes response.

Another object of this invention is to provide in a machine for handling sheetlike material a novel sensing probe capable of discriminating among the presence of a single layer of the sheetlike material, the absence of any sheetlike material, and the presence of two or more superimposed layers of the sheetlike material, and capable of providing a response which is substantially unaffected by machine vibrations.

Another object of this invention is to provide in a web handling machine a novel probe capable of detecting web breakage and capable of providing a response which is substantially insensitive to machine vibrations.

Further objects and advantages of the present invention will be apparent from the following detailed description of a presently preferred embodiment thereof which is shown as applied to a sheet handling machine.

In the drawing:

FIG. 1 is a sectional view, somewhat diagrammatic, illustrating a sheet-handling machine embodying the present invention;

FIG. 2 is an enlarged longitudinal sectional view of the sensing probe in the FIG. 1 machine;

FIG. 3 is a view illustrating schematically the electrical circuit whose operation is controlled by the sensing probe in the sheet-handling machine; and

F l0. 4 illustrates the response of the sensing probe for different conditions when the spacing between the probe and the sheet is changed, such as due to machine vibrations.

Referring to FIG. 1, the present invention is shown as embodied in a sheet-handling machine comprising a metal feedboard or table 10 on which a stream of sheets S, a stream of underlapped sheets in the illustrated embodiment, moves to supply sheets in succession to front register position adjacent the front edge of the feedboard 10 where the sheets are successively registered against a plurality of front stops distributed across the feedboard adjacent its forward edge and including a front stop 11. After engaging the front stops, the sheet is side registered by side-registering mechanism 12 and then moved from the front register position to a cylinder 13 of a printing press. The side-registering mechanism 12 may be of any suitable conventional type. The sheets are advanced from the front register position to the cylinder by feed rolls including a feed-roll segment 14. The front stops are positioned in cutouts, including cutout 15, in the front edge of the feedboard and are movable from a position in the path of a sheet moving down the feedboard, as is shown in FIG. 1, to a position below the surface of the feedboard when the feed rolls are to be operated to advance the sheet in the registered position to the cylinder 13. The cylinder 13 includes gripper means 16 which receive the sheet and carry the sheet into the printing press.

As the sheet S is gripped by the gripper means 16 and is being pulled from the feedboard 10, the next sheet is advancing underneath the sheet being pulled by the cylinder and the front stops are raised to front register the sheet, and this front registration occurs, inthe type of feeder shown, before the tail of the sheet being pulled by the cylinder 13 clears the front stops 11. If desired, overguide means 18 may be provided in addition to the front stops to catch any sheet which might tend to pass the front stops and to lift the tail of the sheet being advanced to the cylinder 13. Both the overguide means 18 and the front stops are conventional mechanisms and are reciprocated in the known manner between active and inactive positions, and the mechanism for efi'ecting the reciprocation will not be described since it does not per se form a part of the present invention. As the sheets of the stream move to the front register position against front stops 11, the sheets pass a sheet-sensing station at which a sensing probe P detects the arrival of a sheet. The probe P is rigidly attached to the frame of the press in any suitable manner permitting the user to selectively adjust the spacing of the probe from the feedboard 10.

The sheets S may be of paper of various compositions or metal foil, for example. The sheet material has a dielectric constant substantially different from the dielectric constant of air. For most printing press applications the sheet material will have a dielectric constant substantially greater than that of air. Each sheet S will have a predetermined thickness for which the sensing probe P may be adjusted so that the probe can discriminate between a single sheet and two or more superimposed sheets of this predetermined thickness. Also, because the dielectric constant of the sheet material is substantially different from that of air, the probe can discriminate between the presence and the absence of a sheet at the sensing position, as explained hereinafter.

In accordance with the present invention the sensing probe P in the present sheet-handling machine is a combined capacitive and inductive probe.

Referring to FIG. 2, in the presently preferred embodiment the probe P presents a flat, annular, metal electrode 20 at its lower end which is positioned in spaced, confronting, overlying relationship to the sheet 8 which is then at the sensing station. This electrode 20 is one plate of a capacitor whose other plate is the portion of the metal feedboard 10 which supports the sheet at the sensing station. The feedboard 10 at the sensing station preferably is of steel or other electrically conductive material. Preferably, this feedboard 10 is grounded, as shown. The dielectric of this capacitor consists of the material of the sheet S which is then beneath the probe and the air gap between the probe electrode 20 and this sheet. The capacitance of this capacitor will have one value if there is no sheet (but only an air gap) between the probe electrode 20 and the feedboard 10, a second value if there is a single sheet between the probe electrode 20 and the feedboard, and a third value if there are two superimposed sheets between the probe electrode 20 and the feedboard.

As shown in FIG. 2, the capacitive electrode 20 is rigidly attached to the bottom end plate 21 of the probe housing 22. Except for the bottom end plate 21, which is of suitable dielectric material, the housing 22 is of electrically conductive nonmagnetic material and it is grounded to the feedboard 10. The bottom end plate 21 of the probe housing has a centrally located, upwardly extending, annular collar 23 which provides a circular guideway 24 located radially inside the capacitive electrode 20 of the probe. This guideway 24 slidably receives the lower end of an annular coil support 25. This coil support carries a central sleeve 26. An annular inductance coil 27, encased in a suitable dielectric potting compound, is rigidly engaged between the sleeve 26 and the support 25. This coil 27 constitutes an inductive probe element, for purposes explained hereinafter.

The coil support 25 is adjustably positioned within the probe housing 22 for selective adjustment of the position of the coil 27 with respect to the capacitive electrode 20 on the bottom face of the probe. For this purpose an adjusting screw 28 is threadedly mounted in the top end plate 29 of the probe housing. A thrust ball 30 is engaged between the inner end of this adjusting screw and the upper end of the coil support 25. The coil support 25 is biases upward by a plurality of springs 31 which insure that the thrust ball 30 is engaged snugly between the adjusting screw and the coil support. Each of these springs 31 encircles a respective stem 32 having a screwthreaded lower end secured to the central upstanding collar 23 on the bottom end plate of the probe housing. Each stem 32 extends loosely up through a respective opening 33 formed in a laterally outwardly projecting flange 34 on the upper end of the coil support 25. Each stem presents an enlarged head 35 on its upper end for limiting the upward movement of the coil support 25. Each bias spring 31 has its lower end bearing against the top of the collar 23 on the bottom end plate 21 of the probe housing and its upper end bearing against the underside of the flange 34 on the coil support. With this arrangement, the position of the coil 27 with respect to the capacitive electrode 20 may be adjusted by turning the adjusting screw 28.

The inductance probe element or coil 27 and the capacitive probe element or plate 20 in the probe are interconnected electrically as shown schematically in FIG. 3. The capacitive probe electrode 20 and the grounded feedboard provide the opposite plates of a capacitor and the dielectric between these capacitor plates is provided by the sheet S and the air gap between the sheet and electrode 20. One end of the coil 27 is connected directly to the capacitive probe electrode 20, and the opposite end of coil 27 is grounded to the feedboard 10. Accordingly, the coil 27 is connected electrically in parallel with the aforementioned capacitor.

The probe coil 27 is inductively coupled to a coil 37 at one end of a coupling loop 38. This coupling loop presents a coil 39 at its opposite end which is inductively coupled to a coil 40. Coil 40 is connected across a capacitor 41 to provide a tuned circuit at the input side of a diode detector 42. Coil 40 is also inductively coupled to a coil 43 connected across a capacitor 44 to provide a tuned output circuit for an oscillator 45. Both the oscillator and the detector are conventional and need not be described in detail. The tuned circuit 43, 44 of the oscillator and the tuned circuit 40, 41 of the detector are both tuned to the same frequency, which preferably is a relatively high frequency, such as 700 kc. For a more complete description of probe P reference may be made to copending US. Pat. application Ser. No. 780,798, filed Dec. 3, 1968, in the name of Nathaniel Rothenberg, and assigned to the assignee of the present invention.

The coupling loop 38 provides a low impedance coupling between the probe coil 27 and the tuned input circuit of the detector 42. The loading on the tuned circuit 40, 41 of the detector will depend upon the impedance of the LC circuit constituted by the probe coil 27 and the capacitor whose plates are the probe electrode 20 and the feedboard 10. Any change in this impedance will be reflected through the coupling loop 38 to the coil 40 in the tuned circuit of the detector and it will change the energy flow through the detector. The output of the detector may be amplified and then applied to a meter or any suitable audible or visual signalling device, or to a control circuit which controls the operation of the printing press and the sheet feeder to automatically stop them when the probe senses an abnormality, such as the absence of a sheet or the presence of two superimposed sheets, instead of a single sheet.

In the operation of this probe, the impedance (both resistive and inductive) of the coil 27 is substantially unaffected by the dielectric between it and the feedboard 10. That is, neither the resistance nor the inductive reactance of the coil 27 will change as a result of the absence of a sheet instead of a single sheet S on the feedboard 10, or as a result of the presence there of two superimposed sheets instead of a single sheet. However, both the apparent resistance and the inductive reactance of the coil 27 will vary with the spacing between this coil and the feedboard 10. This has been found to be true, at an oscillator frequency on the order of 700 kc., whether the feedboard is of metal capable of readily conducting magnetic flux, or a substantially nonmagnetic metal, such as brass or aluminum. The closer this spacing, the greater will be the coil impedance. Consequently, it will be evident that machine vibrations which are imparted to either or both the probe coil 27 and the feedboard l0, and which will change the spacing between them, will change the coil impedance.

Such vibrations will also change the spacing between the capacitive electrode 20 of the probe and the feedboard 10. The capacitive impedance, X,, of the capacitor which consists of electrode 20, feedboard l0, and the dielectric between them will vary with changes in the spacing between the capacitor plates 20 and 10 because this spacing determines the thickness of the airgap which is part of the dielectric of this capacitor. The closer this spacing the smaller will be this capacitive reactance, X

By appropriate adjustment of the position of the probe coil 27 with respect to the capacitive electrode 20 and the position of the capacitive electrode 20 with respect to the feedboard 10 in the absence of machine vibrations, the overall impedance of the LC circuit provided by the probe and the feedboard can be made substantially constant over a range of different spacings between the capacitive electrode 20 and the feedboard 10 such as might be caused by the vibrations normally produced by a printing press, for example. Over this entire range, the rate of change of the capacitive reactance is substantially equal and opposite to the rate of change of the inductive impedance, so that the net impedance of the probe LC circuit remains substantially unaffected by positional changes between the probe and the feedboard, such as might be caused by machine vibrations.

At the same time the capacitive reactance is provided by the probe electrode 20 and the feedboard 10 will be dependent upon the composition of the dielectric between the capacitive probe electrode 20 and the feedboard 10. That is, this capacitive reactance will depend upon how much of the space between the capacitor electrodes 20 and 10 is occupied by sheet or web material and how much is occupied by air. Accordingly, the presence of a single sheet S will cause this capacitive reactance to have a certain value which is noticeably different from the capacitive reactance if no sheet S is present (in which case the dielectric of the capacitor consists entirely of the airgaP). or from the capacitive reactance if two or more superimposed sheets are present.

FIG. 4 shows the output voltage V of the detector plotted against the distance or displacement of the probe from the feedboard 10 for a given position of the probe coil 27 with respect to the capacitive probe electrode 20. it can be seen that this output voltage is substantially constant between displacement positions d and d,. In practice these displacement positions d, and d can be 0.010 inch apart, for example, so that the probe can accommodate this much machine vibration without having a significant efiect on its response to the capacitance of the material between the capacitive probe electrode 20 and the feedboard 10.

In FIG. 4, the curve V, shows the output voltage of the detector when the probe coil impedance is held constant and the capacitance of the capacitor 20, is allowed to vary with the displacement of the probe from the feedboard 10. Conversely, the curve V shows the output voltage of the detector when this capacitance is held constant and the probe coil impedance is allowed to vary with the displacement of the probe from the feedboard.

It should be understood that, for any selected displacement of the probe from the feedboard 10, the position of the probe coil 27 with respect to the capacitive probe electrode 20 must be adjusted to substantially balance the respective rates of change of capacitive reactance and inductive impedance due to spacing changes between the probe and the feedboard. Such balancing of the probe can be performed by routine experimentation. In general, the greater the normal spacing of the probe from the feedboard, the wider will be the range of vibrations over which the probes impedance will remain substantially constant, but the lower will be the level of the output signal from the detector. The level of the output signal can be adjusted by providing a DC level adjust circuit in the detector.

From the foregoing, it will be evident that the disclosed embodiment of the present invention provides a sheet-detecting arrangement operating upon the principle of a capacitive probe to discriminate among (1) the presence of a single sheet, (2) the absence of any sheet, and (3) the presence of two or more superimposed sheets instead of a single sheet. In addition, the probes response is substantially unaffected by a normal level of machine vibrations because of the mutually offsetting inductive and capacitive impedance changes, as described.

It will be evident from the foregoing description that the disclosed probe may be used on a web handling machine, such as a web press, to detect web breakage and to stop the machine in the event of web breakage.

Also, the present probe may be used in a sheet handling machine to detect the presence of scrap material in paper sheets being fed to a press, in which case it will be preferable to provide several such probes spaced apart laterally across the path of the sheets. Also, the present probe may be used in a machine for feeding cardboard or the cover material for books or the like, or to detect the application of a cloth strip in an end sheet combiner, or in a sheet or web handling machine to determine the moisture content of the paper.

Accordingly, while a presently preferred embodiment has been described in detail with reference to the accompanying drawing, it is to be understood that various modifications, adaptations and omissions which depart from the disclosed embodiment may be adopted without departing from the scope of the invention.

We claim:

1. In a machine for feeding a stream of sheets of sheet material to a sensing station which includes an electrically conductive member, apparatus for detecting a misfeed of said sheets at said sensing station comprising: a sensing probe at said sensing station comprising capacitive electrode means cooperating with said conductive member to fonn a capacitor for sensing sheet material between said electrode means and said conductive member, and compensation means responsive to vibration induced changes in distance between the electrode and the conductive member for compensating for the I variations of the capacitance reaction between the electrode and the conductive member caused by said changes in distance.

2. In a machine according to claim 1, wherein said compensation means comprises a coil whose impedance varies inversely with said capacitive reactance changes but is substantially unaffected by the sheetlike material at the sensing station.

3. A machine for handling sheetlike material comprising a support, means for advancing the material along a predetermined path across said support at a sensing station, said support being of electrically conductive material, a sensing probe, means for supporting said sensing probe at said sensing station on the opposite side of said path from said support, said probe having a capacitive electrode spaced from said path by an airgap and in confronting relationship to said support, said capacitive electrode and said support coacting to provide opposite plates of a capacitor between which the sheetlike material is advanced, said capacitor having a capacitive reactance which varies with the thickness of the sheetlike material on the support opposite the probe and with the spacing between said electrode and said support, said probe also including a coil means and means for supporting said coil means in a confronting relationship to said support so that one side of the sheetlike material faces said coil means and the opposite side faces said support, said coil means having an impedance which is substantially unaffected by the presence of sheetlike material on said support opposite the probe but which varies with changes in the spacing between said coil means and said support, said variation of said impedance of said coil means due to spacing changes being inversely related to the changes in the capacitive reactance of said capacitor caused by such spacing changes.

4. A machine according to claim 3, and further comprising means for selectively adjusting the spacing between said capacitive electrode and said coil means in the probe.

5. A machine according to claim 3, wherein said capacitor and said coil means are connected electrically to provide an LC circuit, and further comprising means for detecting changes in the impedance of said LC circuit.

6. A machine according to claim 5, wherein one end of said coil means is directly connected to said capacitive probe electrode and the opposite end of said coil is connected directly to said support.

7. In combination:

a sheet or web handling machine comprising a printing press, an electrically conductive support and means for advancing sheet or web material along a predetermined path across said electrically conductive support at a sensing station;

and a sensing probe, means for supporting said sensing probe at said sensing station on the opposite side of said path in which said material advances from said support, said probe including a capacitive electrode, and means for supporting said capacitive electrode at a location spaced from said path by an airgap and in confronting relationship to said support, said capacitive electrode and said support coacting to provide opposite plates of a capacitor, said capacitor having a capacitive reactance which varies with the thickness of the sheet or web material on the support opposite the probe and with the spacing between said electrode and said support, said probe further including a coil means and means for supporting said coil means in a spaced, confronting relationship to said support so that one side of said material faces said support, said coil means having an impedance which is substantially unaffected by sheet or web material on the support opposite the probe but which varies with changes in the spacing between the coil means and the support, said variation of said impedance of said coil means due to spacing changes being inversely related to the changes in the capacitive reactance of said capacitor caused by such spacing changes.

8. The combination of claim 7, wherein said capacitor and said coil means are connected electrically to provide an LC circuit, and further comprising means for detecting changes in the impedance of said LC circuit.

9. The combination of claim 8, wherein one end of said coil means is directly connected to said capacitive probe electrode and the opposite end of said coil means is connected directly to the support means.

10. The combination of claim 9, and further comprising means for selectively adjusting the position of said coil means with respect to said capacitive electrode in the probe. 

1. In a machine for feeding a stream of sheets of sheet material to a sensing station which includes an electrically conductive member, apparatus for detecting a misfeed of said sheets at said sensing station comprising: a sensing probe at said sensing station comprising capacitive electrode means cooperating with said conductive member to form a capacitor for sensing sheet material between said electrode means and said conductive member, and compensation means responsive to vibration induced changes in distance between the electrode and the conductive member for compensating for the variations of the capacitance reaction between the electrode and the conductive member caused by said changes in distance.
 2. In a machine according to claim 1, wherein said compensation means comprises a coil whose impedance varies inversely with said capacitive reactance changes but is substantially unaffected by the sheetlike material at the sensing station.
 3. A machine for handling sheetlike material comprising a support, means for advancing the material along a predetermined path across said support at a sensing station, said support being of electrically conductive material, a sensing probe, means for supporting said sensing probe at said sensing station on the opposite side of said path from said support, said probe having a capacitive electrode spaced from said path by an airgap and in confronting relationship to said support, said capacitive electrode and said support coacting to provide opposite plates of a capacitor between which the sheetlike material is advanced, said capacitor having a capacitive reactance which varies with the thickness of the sheetlike material on the support opposite the probe and with the spacing between said electrode and said support, said probe also including a coil means and means for supporting said coil means in a confronting relationship to said support so that one side of the sheetlike material faces said coil means and the opposite side faces said support, said coil means having an impedance which is substantially unaffected by the presence of sheetlike material on said support opposite the probe but which varies with changes in the spacing between said coil means and said support, said variation of said impedance of said coil means due to spacing changes being inversely related to the changes in the capacitive reactance of said capacitor caused by such spacing changes.
 4. A machine according to claim 3, and further comprising means for selectively adjusting the spacing between said capacitive electrode and said coil means in the probe.
 5. A machine according to claim 3, wherein said capacitor and said coil means are connected electrically to provide an LC circuit, and further comprising means for detecting changes in the impedance of said LC circuit.
 6. A machine according to claim 5, wherein one end of said coil means is directly connected to said capacitive probe electrode and the opposite end of said coil is connected directly to said support.
 7. In combination: a sheet or web handling machine comprising a printing press, an electrically conductive support and means for advancing sheet or web material along a predetermined path across said electrically conductive support at a sensing station; and a sensing probe, means for supporting said sensing probe at said sensing station on the opposite side of said path in which said material advances from said support, said probe including a capacitive electrode, and means for supporting said capacitive electrode at a location spaced from said path by an airgap and in confronting relationship to said support, said capacitive electrode and said support coacting to provide opposite plates of a capacitor, said capacitor having a capacitive reactance which varies with the thickness of the sheet or web material on the support opposite the probe and with the spacing between said electrode and said support, said probe further including a coil means and means for supporting said coil means in a spaced, confronting relationship to said support so that one side of said material faces said support, said coil means having an impedance which is substantially unaffected by sheet or web material on the support opposite the probe but which varies with changes in the spacing between the coil means and the support, said variation of said impedance of said coil means due to spacing changes being inversely related to the changes in the capacitive reactance of said capacitor caused by such spacing changes.
 8. The combination of claim 7, wherein said capacitor and said coil means are connected electrically to provide an LC circuit, and further comprising means for detecting changes in the impedance of said LC circuit.
 9. The combination of claim 8, wherein one end of said coil means is directly connected to said capacitive probe electrode and the opposite end of said coil means is connected directly to the support means.
 10. The combination of claim 9, and further comprising means for selectively adjusting the position of said coil means with respect to said capacitive electrode in the probe. 